We report the preparation of ordered porous carbon materials with tailored pore sizes selected between 16 and 108 nm using bottlebrush block copolymers (BBCPs) as templates. The nanoporous carbons are prepared via the cooperative assembly of polydimethylsiloxane-block-poly(ethylene oxide) (PDMS-b-PEO) BBCPs with phenol−formaldehyde resin yielding ordered precursor films, followed by carbonization. The assembly of PDMS-b-PEO BBCPs with the resin leads to films exhibiting a spherical morphology (PDMS as the minor domain) with uniform domain sizes between 18 and 150 nm in the bulk. The assembled PDMS sphere diameters scale linearly with BBCPs molecular weights, allowing precise control of domain size. Access to very large ordered domains is an enabling hallmark of BBCPs self-assembly, but reports of well-ordered spherical domains are not common. Carbonization of the ordered precursor films yields nanoporous carbon with uniform and tunable pore size. These nanoporous carbons are shown to exhibit excellent performance as supercapacitor electrodes with capacitance reaching up to 254 F g −1 at a current density of 2 A g −1 .
Carbonization
by rapid thermal annealing (RTA) of precursor films
structured by a brush block copolymer-mediated self-assembly enabled
the preparation of large-pore (40 nm) ordered mesoporous carbon (MPC)-based
micro-supercapacitors within minutes. The large pore size of the fabricated
films facilitates both rapid electrolyte diffusion for carbon-based
electric double-layer capacitors and conformal deposition of V2O5 without pore blockage for pseudocapacitors.
The pores were templated using bottlebrush block copolymers (BBCPs) via cooperative assembly of phenol-formaldehyde resin to
produce microphase-segregated carbon precursor films on a variety
of substrates. Ultrafast RTA processing (∼50 °C/s) at
elevated temperatures (up to 1000 °C) then generated stable,
conductive, turbostratic MPC films, resolving a significant bottleneck
in rapid fabrication. MPC prepared on stainless steel at 900 °C
demonstrated exceptionally high areal and volumetric capacitances
of 6.3 mF/cm2 and 126 F/cm3 (at 0.8 mA/cm2 using 6 M KOH as the electrolyte), respectively, and 91%
capacitance retention after 10,000 galvanostatic charge/discharge
cycles. Post-RTA conformal V2O5 deposition yielded
pseudocapacitors with 10-fold increase in energy density (20 μW
h cm–2 μm–1) without adversely
affecting the high power density (450 μW cm–2 μm–1). The use of RTA coupled with BBCP
templating opens avenues for scalable, rapid fabrication of high-performance
carbon-based micro-pseudocapacitors.
Silicon
carbide (SiC) and silicon oxycarbide (SiOC) ceramic/carbon
(C) nanocomposites are prepared via photothermal pyrolysis of cross-linked
polycarbosilanes and polysiloxanes using a high-intensity pulsed xenon
flash lamp in air at room temperature to yield crystalline and amorphous
phases of SiC and SiOC ceramics, graphitic, and amorphous carbon phases.
The millisecond duration of the radiation pulse is shorter than the
thermal equilibrium time of the preceramic polymers (PCPs), enabling
pyrolysis of the precursor phase and crystallization of the product
before significant energy transfer to the substrate, making this process
uniquely amenable to ceramic processing on or adjacent to thermally
sensitive materials. Rapid precursor pyrolysis and product crystallization
during flash lamp processing, even in air, limit oxidation of the
resulting ceramics. To prepare the nanocomposites, PCPs are coated
onto woven carbon fiber fabrics, thermally cross-linked, and then
flash-lamp-pyrolyzed. The resulting nanocomposites are thermally and
oxidatively stable at extremely high temperatures. The nanocomposites
exhibit excellent performance as supercapacitor electrodes with capacitance
as high as 27.2 mF/cm2 at a 10 mV/s scan rate at room temperature,
excellent stability over 1000 cycles, and Coulombic efficiency of
80%. Patterned nanocomposites are prepared via nanoimprint lithography,
followed by photothermal processing of precursor films. These nanocomposites
have potential applications in energy storage, catalysis, and separations.
We demonstrate SDN-controlled dynamic front-haul optical network pro visioning and modulation format adaptation, running on an emulation of the COSMOS testbed benchmarked against the COSMOS hardware testbed.
We report a method for fast, efficient, and scalable preparation of high-quality, large area, few-layer graphene films on arbitrary substrates via high-intensity pulsed xenon flash lamp photothermal pyrolysis of thin precursor films at ambient conditions in millisecond time frames. The precursors comprised poly(2,2-bis(3,4-dihydro-3-phenyl-1,3-benzoxazine)), and cyclized polyacrylonitrile and possess significant absorption cross section within the bandwidth of the emission spectrum of a xenon flash lamp. By localizing light absorption to the precursor films, the process enabled the preparation of few-layer graphene films on any substrate, including thermally sensitive substrates without the need for any catalytic substrate as in chemical vapor deposition-based approaches or conductive electrodes as in electrochemical methodbased approaches. The extent of conversion of the precursor films to graphene was strongly dependent on pulse energy and the local temperature achieved due to photothermal effect, which were controlled via pulse power modulation; it also depended on structural properties of the precursor and to a lesser extent on the substrate. The cPAN showed a higher efficiency for conversion to graphene, as confirmed by Raman spectra (I D /I G ∼ 0.3), and sheet resistance of 0.1 Ω cm. To demonstrate the utility of the process, graphene film electrodes prepared photothermally on carbon fiber current collector were used for the fabrication of micro-supercapacitors with a very high areal supercapacitance of 3.5 mF/cm 2 . Subsequent deposition of manganese oxide onto the fabricated electrodes significantly increased the energy storage capability of the supercapacitor, yielding a device with exceptionally high capacitance of 80 F/g at 1 mA current, good rate capability, and long cycle life.
The miniaturization of electronic devices led to the advent of on-chip power sources with high energy and power density requirement. The development of such miniaturized energy devices further requires the preparation and/or processing of thin films (down to a few nanometers) of active material. Mesoporous carbon possessing both high porosity and conductivity are desired for such applications. However, obtaining thin films of mesoporous carbon on various substrates using commercially viable approaches requires further improvement and investigation.
We have adapted rapid thermal annealing (RTA) as a novel approach to obtain mesoporous carbon. RTA enables rapid heating to temperatures up to 1200oC in just a few seconds and therefore provides a route for complete carbonization within a few minutes. Carbon precursor films comprised of brush block copolymers (BBCP) as sacrificial templates and phenol formaldehyde (PF) resin as a carbon source were prepared. In particular, the self-assembly of polydimethylsiloxane-b-polyethylene oxide (PDMS–b-PEO) BBCP and PF resin led to the formation of microphase-segregated film on various substrates including Si wafer, fused silica, and stainless steel. The PDMS domain in the BBCP fostered strong adhesion to the substrate even after annealing. RTA enabled complete carbonization of the precursor film within only 5 minutes, whereas conventional methods require approximately 500 minutes. Rapid processing at 1000oC resulted in the formation of mesoporous carbon with higher degree of graphitization, which is difficult to achieve with conventional carbonization method. The device prepared via RTA has a capacitance value of 7.0 mF/cm2 at 100mV/s, which is one of the highest values obtained for nanometer-thick carbon-based electrodes. These electrodes maintained a quasi-rectangular shape during the potential vs current scan, even at a scan rate of 20 V/s, which suggests that these materials are promising candidates for applications requiring very high-power density.
The mesoporous carbon structure having high porosity and high conductivity can be further utilized as supports for the deposition of pseudo-capacitance materials to further boost the energy density of the device.
Figure 1
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